1. Field of the Invention
The present invention relates to a diaphragm used for a speaker device and a manufacturing method thereof.
2. Description of Related Art
There is known a diaphragm for a speaker made of acrylic foam, and an example thereof is disclosed in Published Japanese Translation of a PCT Application Laid-open under No. 2004-537243 (Reference-1). In the diaphragm for the speaker according to the Reference-1, poly(mete)acrylimide foam is used as a core layer.
As for the poly(mete)acrylimide foam, since the coefficient of saturated water absorption is high (substantially 30 wt %), decrease of strength caused by the water absorption is large. Therefore, when it is applied to the diaphragm for the speaker, if the speaker is used in a humid environment, sound quality deterioration caused by the decrease of strength is large. Particularly, when this diaphragm is used for an on-vehicle speaker and/or a marine speaker, the deterioration of the strength and the sound quality due to the water absorption is remarkable.